1 Arches National Park is in Utah. The park protects many geologic formations. It is famous for the arches. There are other unusual formations. There are fins, spires, and balanced rocks. The park is in the high desert. The summers are very hot. The winters are cold. Very little rain falls. The greatest number of arches in the world is here.2 There are over 2,000 sandstone arches in the park. An arch must have at least a three foot opening to be called an arch. The longest arch in the park is Landscape Arch. It is 306 feet from base to base. The arches formed over millions of years. This area was once covered by a sea. The sea evaporated. Water again covered the area. This cycle happened many times. The salt and sand that was left behind became rock. The salt bed buckled. Some surfaces rose up. Others fell down to cause holes. Vertical cracks formed. The cracks eventually became arches. Erosion helped form the arches. Water carried the debris away. Ice made cracks in the rocks get bigger. All of this left behind the unusual rock formations visitors can see today.